1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electrophotographic copier or a laser printer, and a process cartridge detachably mountable to this apparatus.
2. Related Background Art
Conventionally, for an image forming apparatus that performs an electrophotographic image forming process, a process-cartridge system is employed for which process means (a process unit), which acts on an electrophotographic photosensitive body that serves as an image bearing member, is an integrally formed component of a cartridge that can be detachably mounted within the main body of an image forming apparatus. The use of such a cartridge provides a considerable improvement in operability, because apparatus maintenance can be performed by the user. As a result, cartridge-process systems are widely employed for image forming apparatuses today.
Presently, depending on the application, multiple types of process units are employed for the process cartridge that is mounted within the main body of an image forming apparatus.
For this process cartridge, however, since manufacturing dispersions tend to affect the capabilities of multiple process units, the margin allowed for maintaining image quality is increased, which imposes a great restriction on the determination of the process condition.
An example electrophotographic image forming apparatus that employs a contact charging device will now be described while referring to FIG. 5.
A photosensitive drum 101, which is an electrophotographic photosensitive body, is rotated in a direction indicated by an arrow A while its surface is charged by a charge roller 120, which is an electrically coupled charging means that, by the application of a predetermined force, is pressed against and rotates with the photosensitive drum 101. To charge the photosensitive drum 101, a power source 121, as a power supply means, supplies a vibration voltage (vibration bias), obtained by the superimposition of an alternating-current bias and a direct-current bias, to the charge roller 120. Once the surface of the photosensitive drum 101 has been uniformly charged in this manner, in accordance with image data, a laser beam L forms an electrostatic latent image thereon.
Thereafter, a developing device 110, which is developing means, attaches a toner T, which is a developer, to the electrostatic latent image on the photosensitive drum 101, forming a toner image that is transferred to a recording sheet 104, composed of a transferring material, by a transfer roller 102. The recording sheet 104 is then conveyed to a fixing apparatus (not shown) at which it is heated to permanently fix the toner image to the recording sheet 104.
Once the transfer process has been completed, a cleaner 131, which is cleaning means, removes residual toner from the photosensitive drum 101, and prepares the photosensitive drum 101 for use for image forming.
In this example, the photosensitive drum 101, the charge roller 120, the developing device 110 and the cleaner 131 are integrally formed components of a process cartridge B that, by using attachment means 150, is detachably mounted within the main body of the image forming apparatus.
Two different formulas or manufacturing methods are used for fabricating the charge roller 120 employed for the image forming apparatus in this example. According to the first formula (formula A), for the charge roller 120, a rubber layer is formed by using a rubber, such as EPDM, wherein carbon is dispersed, and according to the second formula (formula B), a rubber layer is formed by using polyurethane rubber wherein carbon is dispersed.
When a different formula is used to form the charge roller 120, the following problem occurs.
Since, as is shown in FIG. 3, the characteristics of the formulas used for the charge roller 120 differ, the electrical properties will also vary. And because of the dispersion in the electrical properties, the amount of discharge current, which greatly affects the service life of the photosensitive drum 101, will be altered. And finally, the service life of the photosensitive drum 101 will also differ due to the difference in the charge roller 120. That is, a dispersion will also appear in the service life of the process cartridge B.
Then, since a characteristic such as the charging performance is also varied, the potential applied to the photosensitive drum 101 is changed, and there is a dispersion in the image quality.
As is described above, when the formula for the charge roller differs, a dispersing occurs in the service life of the photosensitive drum or the process cartridge that also affects the image quality.
It is, therefore, one objective of the present invention to provide a process cartridge and an image forming apparatus, wherein a change in potential at an image bearing member, which is due to a charging member, is reduced.
It is another objective of the present invention to provide a process cartridge and an image forming apparatus for which information concerning the type of charging member employed is stored in storage means.
It is an additional objective of the present invention to provide a process cartridge and an image forming apparatus for which dispersions in the service lives of the image bearing member and the process cartridge that are due to a charging member are eliminated.
It is a further objective of the present invention to provide a process cartridge and an image forming apparatus whereby and wherein, for an extended period of time, images can be stably formed for which there are no dispersions in quality that are due to a charging member.
Other objectives and features of the invention will become apparent during the course of the following detailed explanation, given while referring to the accompanying drawings.